Disclosed is a visual display system and a method for displaying information. The information displayed on the visual display system may be substantially or entirely immune to stray electric fields.
Traditional signs have been based upon printed materials, paper, plastic, metal, etc., and are therefore not programmable. Accordingly, they are not easily changed. In an attempt to overcome this problem, electronically programmable and/or controllable signs have been developed. For example, liquid crystal diode (LCD) displays, cathode ray tube (CRT) displays, and other electrically-addressable displays will display an image in response to applied electric signals or fields. However, such signs typically require a large amount of electricity, since they must provide illumination in order to be visible to a viewer.
Other types of electric writeable media known as rotatable element displays or electric paper displays also exist. One example of a rotatable element display includes a polymer substrate and bichromal rotatable elements such as balls or cylinders that are in suspension with an enabling fluid and are one color, such as white, on one side and a different color, such as black, on the other. Examples of such rotatable element displays are described, for example, in U.S. Pat. No. 5,723,204 to Stefik and U.S. Pat. No. 5,604,027 to Sheridon, each of which is incorporated herein by reference in its entirety. Under the influence of an electric field, the elements rotate so that either the white side or the black side is exposed.
Another type of electric writeable media is known as an electronic ink display, such as the one described in U.S. Pat. No. 6,518,949 to Drzaic, which is incorporated herein by reference. An electronic ink display includes at least one capsule filled with a plurality of particles, made of a material such as titania, and a suspending fluid containing dye. When a direct-current electric field of an appropriate polarity is applied across the capsule, the particles move to a viewed surface of the display and scatter light. When the applied electric field is reversed, the particles move to the rear surface of the display and the viewed surface of the display then appears dark.
Yet another type of electric writeable media, also described in U.S. Pat. No. 6,518,949 to Drzaic, includes a first set of particles and a second set of particles in a capsule. The first set of particles and the second set of particles have contrasting optical properties, such as contrasting colors, and can have, for example, differing electrophoretic properties. The capsule also contains a substantially clear fluid. The capsule has electrodes disposed adjacent to it connected to a voltage source, which may provide an alternating-current field or a direct-current field to the capsule. Upon application of an electric field across the electrodes, the first set of particles move toward one electrode, while the second set of particles move toward the second electrode.
Other examples of writeable media include liquid crystal diode displays, encapsulated electrophoretic displays, and other displays.
Rotatable element displays have numerous advantages over conventional displays, such as LCDs and CRTs, since they are suitable for viewing in ambient light, they retain an image for long periods of time in the absence of an applied electric field, and they can be made to be very lightweight and/or flexible. For further advantages of such displays, see U.S. Pat. No. 5,389,945 to Sheridon, incorporated herein by reference in its entirety. An example of such a display is a SmartPaper™ display from Gyricon LLC.
FIG. 1 depicts the switching behavior of electric paper. The electric paper includes a plurality of rotatable elements, such as bichromal balls. The bichromal balls (10) have a first-colored hemisphere (12), such as black, and a second-colored hemisphere (14), such as white. Typically, the black hemisphere (12) is positively charged and the white hemisphere (14) is negatively charged. As such, the bichromal ball has an electrical dipole charge that causes it to rotate upon the application of an external electric field.
In bichromal balls, the charge of one hemisphere is often greater magnitude than the charge of the other hemisphere. Thus, each bichromal ball has an electrical monopole charge, which is defined as the algebraic sum of the hemispherical charges. The electrical monopole charge permits a ball to move across the cavity (14) when an external electric field is applied.
During quiescent periods, a combination of electrical, hydraulic and mechanical forces may attach a bichromal ball to a wall (e.g., 16, 16′) of a cavity in which it resides. The electrical monopole charge causes the bichromal ball to separate from a cavity wall (e.g., 16) and move to the opposite cavity wall (e.g., 16′) in the presence of an external electric field. Once free from the cavity wall, the electrical dipole charge interacts with the external electric field to cause the bichromal ball to rotate into alignment with the electric field. When the bichromal ball reaches the opposite cavity wall (e.g., 16′), it attaches to the wall and rotation ceases. Accordingly, the electrical monopole charge has been recognized as a component in prior art electric paper switching behavior.
One disadvantage of electric paper displays is that they may be subject to stray electric fields, such as those caused by static electricity generated from handling papers or walking across carpets. Such stray electric fields, when generated proximate to electric paper, may cause rotatable elements within the electric paper to rotate, or other bichromal media to change, unintentionally. As a result, the image displayed on the electric paper may become corrupted.
As such, a need exists to improve electric displays, such as electric paper, by disabling the effects of stray electric fields upon changeable bichromal display media in the electric display.